A medical device may carry a load, such as, for example, a radiation emitting device or a patient. Radiation emitting devices are generally known and used, for instance, as radiation therapy devices for the treatment of patients. A radiation therapy device generally may include a gantry which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator is located within the gantry for generating a high energy radiation beam for therapy. This high energy radiation beam may be an electron beam or photon (x-ray) beam, for example.
Another example of a medical device carrying a load is a computed tomography apparatus of the type having a gantry that is rotatable around a rotational axis. An example of such a computed tomography apparatus is disclosed, for example, in U.S. Pat. No. 5,610,968. The computed tomography apparatus has a gantry mounted to be rotatable around a rotational axis and at which the components such as, for example, an X-ray source or a radiation detector that rotate around a patient under examination together with the gantry during operation of the gantry, are arranged.
A further example of a medical device is described in EP 1837049. Such a device comprises at least one drive means (a positioner) for positioning a load, such as a particle beam device. In such a device it is likely that if a system error is detected, then a mechanical brake device will engage and hold the load.
Brake failure in prior art devices and methods is typically mitigated by selecting a “fail-safe” brake and using of a second brake directly on the load. This leads to increasing standard cost in realizing such devices and methods.
A commonly used driving means in the prior art is a ball screw with a single fail-safe brake. For example, for a camera system motion implementation using high efficiency ball screws to move extremely heavy loads with motors driven by amplifiers that are shared with other axes. A single “fail-safe” brake is used to hold the load stationary when, for example, not driven by the motor or during a loss of power. If the brake were to fail, then the load would fall due to the force of gravity acting upon the load. This could result in severe injury.
A load carrying device within the field of medicine for carrying a patient, such as a mechanism moving a patient table top or a bed is known. Such a patient table top is, for example, described in U.S. Pat. No. 4,885,998.
A majority of devices in the prior art typically mitigates brake failure by first selecting of a “fail-safe” brake and thereafter using of a second brake directly on the load. Hereby the standard costs increase.
There are certain prior art camera system motion implementations that employee high efficiency ball screws to move extremely heavy loads with motors driven by amplifiers that are shared with other axes. A single “fail-safe” brake is used to hold the load stationary when not driven by the motor or during a loss of power. If the brake were to fail, then the load would fall due to the force of gravity acting upon the load and severe injury could result. When considering the possible failure modes of a single “fail-safe” brake implemented in a ball-screw driven axis (such as the radial axis), the associated system response may be one or more of the following:
(A) Brake fails to release. This may result in no hazard.
(B) Brake fails to engage at the end of movement. This may result in that the motion system kills power upon detection of unintended motion and the load falls.
(C) Brake holding power degrades over time, resulting in slippage. This may result in that the motion system kills power and the load either comes to a stop after moving a greater than expected distance or slowly falls due to continuous brake slippage.
(D) Catastrophic brake failure, with the system powered, stationary and not in a stationary state, resulting in unintended release of the load. This may result in the load falling.
(E) Catastrophic brake failure, with the system not powered, or in a stationary state, resulting in unintended release of the load. This may result in the load falling.
In view of the prior art discussed above, there is a need to provide a method and system allowing for a more safe manner to mitigate brake failure. Additionally, such a method and system should preferably be inexpensive to realize. There is also a need to improve the mitigation of brake failure in existing devices. This would allow for a safe medical device carrying loads without causing any mechanical damage or personal injury.
There is a need that existing methods and systems taking advantage of existing system motion features could result in a more accurate positioning of medical devices in relation to patients, because improved reliability and accuracy of a brake system. Good spatial information of the relevant part of the medical device needs to be assessed. Hereby patients could be treated in a more target-specific manner resulting in, for example, reduced radiation dosage when X-rayed.
There also exists a need to minimize the structure of the medical device by avoiding the need for extra safety devices, such as extra brakes. The construction of the medical device should be simple from a technical and an economical perspective.
Additionally, it is desirable to avoid cumbersome arrangements that would interfere with the available space around the medical device.